<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <button @click='add'>+</button>
        <h1>{{num}}</h1>
        <button @click='sub'>-</button>
    </div>
</body>
<script src="https://cn.vuejs.org/js/vue.js"></script>
<script>
    let vm = new Vue({
        el: "#app",
        data: {
            num: 888
        },
        methods: {
            add: function () {
                this.num += 1;
            },
            sub: function () {
                this.num -= 1;
            }
        }
    });
</script>
</html>